Quantum dot and luminescent material made therefrom

ABSTRACT

A solar concentrator module (80) employs a luminescent concentrator material (82) between photovoltaic cells (86) having their charge-carrier separation junctions (90) parallel to front surfaces (88) of photovoltaic material 84 of the photovoltaic cells (86). Intercell areas (78) covered by the luminescent concentrator material (82) occupy from 2 to 50% of the total surface area of the solar concentrator modules (80). The luminescent concentrator material (82) preferably employs quantum dot heterostructures, and the photovoltaic cells (86) preferably employ low-cost high-efficiency photovoltaic materials (84), such as silicon-based photovoltaic materials.

COPYRIGHT NOTICE

© 2011 Spectrawatt, Inc. A portion of the disclosure of this patentdocument contains material that is subject to copyright protection. Thecopyright owner has no objection to the facsimile reproduction by anyoneof the patent document or the patent disclosure, as it appears in thePatent and Trademark Office patent file or records, but otherwisereserves all copyright rights whatsoever. 37 CFR § 1.71(d).

RELATED APPLICATION

This application is a continuation of and claims the benefit of U.S.patent application Ser. No. 13/287,407, filed Nov. 5, 2011, and issuedon Dec. 20, 2016 as U.S. Pat. No. 9,525,092, which claims the benefitunder 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No.61/410,754, filed Nov. 5, 2010, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to solar modules and, in particular, to a solarmodule employing a luminescent concentrator material.

BACKGROUND INFORMATION

The cost of electricity from relatively efficient solar cells in amodule is still higher in dollar per watt than most currently availableretail peak electricity rates. The conventional wisdom is that cost ofelectricity per watt generated by a solar cell can generally be changedin either of two ways: the light conversion efficiency of the solar cellcan be increased, or the cost of producing the solar cell can bedecreased. More efficient or less expensive solar components in modulesare, therefore, desirable.

SUMMARY OF THE DISCLOSURE

The cost per watt generated by a solar module can be reduced by use of aluminescent concentrator material.

In some embodiments, the percentage of surface area of photovoltaicmaterial in a solar module can be reduced by employing luminescentconcentrator material for some of the surface area of the solar module.

In some alternative or cumulative embodiments, the surface area of thephotovoltaic material is generally parallel to a charge carrier junctionplane within the photovoltaic material and generally covers 43 to 91% ofthe surface area of the solar module.

In some alternative or cumulative embodiments, the surface area ofluminescent concentrator material generally covers 2 to 50% of thesurface area of the solar module.

In some alternative or cumulative embodiments, the luminescentconcentrator material is positioned between photovoltaic cells ofrelatively efficient photovoltaic material to reduce the amount and costof photovoltaic material employed in a solar module.

In some alternative or cumulative embodiments, the photovoltaic cellsemploy wafer-based photovoltaic materials.

In some alternative or cumulative embodiments, the wafer-basedphotovoltaic materials include microcrystalline silicon.

In some alternative or cumulative embodiments, the luminescentconcentrator material includes quantum dot heterostructures.

Additional aspects and advantages will be apparent from the followingdetailed description of preferred embodiments, which proceeds withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional side view of a portion of a standard solar moduleemploying photovoltaic material with its large-area surface dimensionoriented parallel to a bottom layer material.

FIG. 2 is a sectional side view of a portion of a luminescent solarconcentrator module employing luminescent concentrator material and astrip of photovoltaic material with its junction plane orientedperpendicular to the sun-facing surface of the luminescent solarconcentrator module.

FIG. 3 is an isometric view of a luminescent lateral transfer solarconcentrator module employing a luminescent concentrator materialbetween spaced-apart areas of photovoltaic material having its junctionplane oriented parallel to the front surface of the quantum luminescentsolar concentrator module.

FIG. 4A is a sectional side view of a portion of a luminescent lateraltransfer solar concentrator module of FIG. 3 showing a luminescentconcentrator material having a height dimension that is the same as aheight dimension of the photovoltaic material with respect to the bottomlayer material.

FIG. 4B is a sectional side view of a portion of an alternativeluminescent lateral transfer solar concentrator module showing aluminescent concentrator material having a height dimension that isgreater than a height dimension of the photovoltaic material withrespect to the bottom layer material.

FIG. 4C is a sectional side view of a portion of an alternativeluminescent lateral transfer solar concentrator module showing theluminescent concentrator material positioned at level only above thefront surface of the photovoltaic material.

FIG. 4D is a sectional side view of a portion of another alternativeluminescent lateral transfer solar concentrator module showing theluminescent concentrator material positioned at a level only below afront surface of the photovoltaic material.

FIG. 5A is a plan view of an exemplary layout of the surface areas ofphotovoltaic material and luminescent concentrator material in anexemplary luminescent lateral transfer concentrator module.

FIG. 5B is a plan view of an alternative layout of the surface areas ofphotovoltaic material and luminescent concentrator material in anexemplary luminescent lateral transfer concentrator module.

FIG. 6 is simplified enlarged drawing of an encapsulated quantum dotheterostructure.

FIG. 7 is a graph showing external quantum efficiency as a function ofwavelength for photons incident on the luminescent concentrator materialat different distances from an mc-Si cell.

FIGS. 8A, 8B, and 8C are respective graphs of costs per watt versusintercell spacing for QuLLT solar concentrator modules.

FIGS. 9A, 9B, and 9C are respective graphs of costs per watt versusintercell spacing show for dual color QuLLT (DCQuLLT) solar concentratormodules, in which one luminescent concentrator material occupies theintercell region and another luminescent concentrator material, such asa downshift material, overlays the photovoltaic cells.

FIGS. 10A, 10B, and 10C show alternative methods of fabricating QuLLTsolar concentrator modules.

FIG. 11 is a photograph showing an experimental QuLLT submodule that hasbeen built.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a sectional side view of a portion of a standard solar module10 formed of photovoltaic cells 12 employing photovoltaic material 14with its front, top, or sun-facing surface 16 oriented to be parallel toa junction plane of its charge-carrier separation junction 18. Withreference to FIG. 1, the front surfaces 16 have the large-area surfacedimensions of the photovoltaic cells 12 and have a front surface planethat is generally parallel to a back plane of a back protective layer20. The photovoltaic cells 12 are space-apart with intercell areas 22being filled with air between the regions of the photovoltaic material14. In a standard 60-cell solar module 10, the photovoltaic material 14occupies at least 91% of the surface area, the intercell area occupiesabout 2% of the surface area, and the aluminum frame occupies about 7%of the surface area of the standard solar module 10. The photovoltaicmaterial 14 and the intercell area 22 are typically covered by a fronttransparent protective layer 24, such as a sheet of glass.

Many of the photons 32 incident upon the intercell area 22 are reflectedout of the solar module 10 along exemplary reflection paths 34 and 36.Only a limited number of photons 32 incident upon the intercell area 22are reflected internally in a manner, such as along exemplary reflectionpath 38, in which they can be absorbed by the photovoltaic material 14.Most of the photons 32 incident upon the intercell area 22 are reflectedout of the solar module 10.

In some standard solar modules 10, internal reflection is improved byemploying a layer of reflective material 26 above or beneath the backprotective layer 20. A commonly employed reflective material 26 is whiteTedlar™, which is able to scatter approximately 20% of the photons 32that hit it into the photovoltaic material 14 from both its frontsurface 16 and rear surface 28 by total internal reflection (TIR). For afront transparent protective layer 24 above Tedlar™, 25.6% of that 20%of the light that does scatter is below the critical angle for TIR. TIRoccurs when light inside a medium of index of refraction, n₂, hits aninterface with a medium of index of refraction, n₁, at an angle furtherfrom normal than the critical angle. The critical angle is defined asθ=arcsine(n₁/n₂). For the case of glass to air, this angle is 41.8°.

FIG. 2 is a sectional side view of a portion of a luminescent solarconcentrator (LSC) module 40 employing luminescent concentrator material42 and a strip of highly efficient photovoltaic material 44 oriented sothat its junction plane 46 and its junction-parallel surface 47 areperpendicular to a front or sun-facing surface 48 of the photovoltaicmaterial 44, perpendicular to a front or sun-facing surface 50 of theluminescent concentrator material 42, perpendicular to a front orsun-facing surface 52 of the luminescent solar concentrator module 40,and perpendicular to a front or sun-facing surface 54 a bottom layermaterial 56. With reference to FIG. 2, the luminescent concentratormaterial 42 may reflect a greater percentage (with respect to air) ofincident photons 32 along exemplary reflection paths 58 and 60.

The strips of photovoltaic material 44 in a luminescent solarconcentrator module 40 are 1 to 2 mm in width and 1 to 100 cm in length.The luminescent concentrator material 42 occupy regions that rangebetween 1 and 10 cm in width. If one assumes standard kerf losses of 50%of the photovoltaic material 44, then 0.1 to 1 m² of photovoltaicmaterial 44 per m² of luminescent solar concentrator module 40.

Because the relative amount of photovoltaic material 44 is small,causing the relative amount of the sun-facing surface 48 and thejunction-parallel surface 47 to have little relative surface area(typically less than 10%), the luminescent solar concentrator module 40is useful only when highly efficient photovoltaic material 44 such asInGaP is employed. Unfortunately, high volume production costs for InGaPcells are still in the neighborhood of $40,000/m², which isprohibitively expensive at a practical concentration for most practicalapplications. The InGaP cells are sliced into strips, rotatedperpendicular to the incident sunlight, and glued onto the side of theluminescent material 42. The slicing and gluing steps also addmanufacturing complications and reduce yield.

FIG. 3 is an isometric view of an exemplary luminescent lateral transfer(LLT) solar concentrator module 80 employing a luminescent concentratormaterial 82 between spaced-apart areas of photovoltaic material 84 ofthe photovoltaic cells 86. FIG. 4A is a sectional side view of a portionof a luminescent lateral transfer solar concentrator module 80 (shown as80 a in FIG. 4A) taken along lines 4A-4A of FIG. 3. With reference toFIGS. 3 and 4A, the photovoltaic material 84 of the photovoltaic cells86 has a front, top, or sun-facing surface 88 that is oriented to begenerally parallel to a junction plane of its charge-carrier separationjunction 90. Examples of charge-carrier separation junction 90 include,but are not limited to, pn, pin or nip junctions.

The front or sun-facing surface 88 is also generally parallel to a frontor sun-facing surface 74 of a front or sun-facing transparent protectivelayer 76 such as a sheet of glass, generally parallel to a front orsun-facing surface 92 of the luminescent concentrator material 82,generally parallel to a front or sun-facing surface 94 of theluminescent lateral transfer solar concentrator module 80, and generallyparallel to a front or sun-facing surface 96 of a bottom layer material98.

The front surface 88 and an opposing back, rear, bottom, or earth-facingsurface 100 of the photovoltaic material 84 constitute major surfaces ofthe photovoltaic material 84. The photovoltaic material 84 also haswidth-related surfaces 102 that have a width dimension 104 andlength-related surfaces 106 that have a length dimension 108. The widthdimension 104 and the length dimension 108 are typically different;however, if the front surface 88 has a square surface area, then thedimensions 104 and 108 can be generally the same. In someimplementations, the width dimension 104 and the length dimension 108both have the same or different values greater than 2 mm, 5 mm, 10 mm,25 mm, 50 mm, 100 mm, or 150 mm.

The width-related surfaces 102 and the length-related surfaces 106 havesurface areas that are smaller than the surface area of the frontsurface 88 and constitute minor surfaces of the photovoltaic material84. In many implementations, the photovoltaic cells 86 have the samesurface areas and the same width and length dimensions 104 and 108 ofphotovoltaic material 84; however, photovoltaic cells 86 with differentdimensions can be employed.

The front or sun-facing surface 92 and an opposing back, rear, bottom,or earth-facing surface 110 of an intercell region 78 of the luminescentconcentrator material 82 constitute major surfaces of the region 78 ofthe luminescent concentrator material 82. The region 78 of theluminescent concentrator material 82 also has width-related surfaces 112that have a width dimension 114 and length-related surfaces 116 thathave a length dimension 118. In many implementations, the widthdimensions 104 and 114 are the same but the length dimensions 108 and118 are different. The width dimension 114 and the length dimension 118are typically different; however, if the front surface 92 has a squaresurface area, then the dimensions 114 and 118 can be generally the same.The width-related surfaces 112 and the length-related surfaces 116 havesurface areas that are smaller than the surface area of the frontsurface 92 and constitute minor surfaces of the luminescent concentratormaterial 82.

In many implementations, the regions 78 of the luminescent concentratormaterial 82 have the same surface areas and the same width and lengthdimensions 114 and 118 of luminescent concentrator material 82; however,regions 78 of luminescent concentrator material 82 with differentdimensions can be employed. For example, intercell regions 78 a betweenwidth-related surfaces 102 of opposing photovoltaic cells 86 may haveone or more different dimensions than intercell regions 78 b betweenlength-related surfaces 106 of opposing photovoltaic cells 86.Similarly, intercell regions 78 c that connect intercell regions 78 aand 78 b may have one or more different dimensions than each other orone or more different dimensions than those of intercell regions 78 aand 78 b.

The luminescent concentrator material 82 has a height dimension 120 thatmay be the same as or different from a height dimension 122 of thephotovoltaic material 84. In some implementations, the height dimension120 of the luminescent concentrator material 82 is between 1 and 1000microns. In some implementations, the height dimension 120 of theluminescent concentrator material 82 is between 200 and 900 microns, 300and 800 microns, or 400 and 700 microns. In some implementations, therange of height dimensions 120 matches the absorption range of theluminescent concentrator material 82.

FIGS. 4B, 4C, and 4D are sectional side views of portions of respectivealternative exemplary implementations of luminescent lateral transfersolar concentrator modules 80 b, 80 c, and 80 d. With reference to FIG.4B, the luminescent concentrator material 82 of the luminescent lateraltransfer solar concentrator modules 80 b has a height dimension 120 bthat is greater than the height dimension 122 of the photovoltaicmaterial 84.

A spacer material 140 may be employed to occupy the volume 138 betweenthe bottom of protective layer 76 and the front surface 88 of thephotovoltaic material 84, i.e., the spacer material 140 may have aheight dimension 142 that is the difference between the height dimension120 b and the height dimension 122 of the photovoltaic material 84. Thespacer material 140 may have length and width dimensions that matchthose of the photovoltaic material 84. In some implementations, thespacer material is a transparent protective material employed tosafeguard the photovoltaic material 84 without interfering with it lightabsorbing function, and it may be the same or different material as thatoptionally used to encapsulate the entire luminescent lateral transfersolar concentrator module 80. In some implementations, the luminescentconcentrator material 82 may be used as the spacer material 140 to fillthe volume 138, with or without a layer of spacer material 140positioned between the protective layer 76 and the luminescentconcentrator material 82.

With reference to FIG. 4C, the luminescent concentrator material 82 ofthe luminescent lateral transfer solar concentrator modules 80 c ispositioned at a level above the front surface 88 of the photovoltaicmaterial 84 but adjacent to the plane of its side surface 102. Thevolume 138 may include the spacer material 140, or the volume 138 mayinclude the luminescent concentrator material 82 so that a an optionallyuniform sheet of luminescent concentrator material 82 covers both theintercell areas 78 and the photovoltaic material 84. A spacer material140 may be employed to occupy a volume 144 between the bottom surface ofluminescent concentrator material 82 in region 78 and the front surface96 of the bottom layer material 98, i.e., the spacer material 140 mayhave a height dimension 146 that is the same height dimension 122 of thephotovoltaic material 84.

With reference to FIG. 4D, the luminescent concentrator material 82 ofthe luminescent lateral transfer solar concentrator modules 80 d ispositioned in the intercell areas 78 but at a height dimension 120 dthat is less than or equal to the height dimension 122 of thephotovoltaic material 84. The volume 144 may be filled with an spacermaterial 148 that may be the same as or different from the spacermaterial 140.

FIGS. 5A and 5B are plan views of exemplary alternative layouts 150 aand 150 b of exemplary luminescent lateral transfer concentrator modules80. With reference to FIGS. 5A and 5B, the photovoltaic cells 86 areshown to be relatively square in shape and have an exemplary frontsurface 88 with a length dimension 108 of 156 mm. However, the widthdimensions 104 and the length dimensions 108 need not be the same andcan be any standard or nonstandard size. For example, the dimensions maybe consistent with those of a standard mc-Si photovoltaic cells or astandard CIGS photovoltaic cells 86. In some implementations, thephotovoltaic cells 86 may have nonrectangular surface areas, such ascircular. Such nonrectangular surface areas may be represented by thediameter, radius, or other major dimensions.

In some implementations, the cumulative exposed surface area of thefront surfaces 88 can range between 43% and 91% of the total frontsurface area of the luminescent lateral transfer concentrator modules80. In some implementations, the cumulative exposed surface area of thefront surfaces 88 can range between 43% and 75% of the total frontsurface area of the luminescent lateral transfer concentrator modules80. In some implementations, the cumulative exposed surface area of thefront surfaces 88 can range between 43% and 55% of the total frontsurface area of the luminescent lateral transfer concentrator modules80. In some implementations, the cumulative exposed surface area of thefront surfaces 88 is less than 50% of the total front surface area ofthe luminescent lateral transfer concentrator modules 80.

In some implementations, the cumulative exposed surface area of thefront surfaces 88 can range between 55% and 91% of the total frontsurface area of the luminescent lateral transfer concentrator modules80. In some implementations, the cumulative exposed surface area of thefront surfaces 88 can range between 75% and 91% of the total frontsurface area of the luminescent lateral transfer concentrator modules80. In some implementations, the cumulative exposed surface area of thefront surfaces 88 is greater than 50% of the total front surface area ofthe luminescent lateral transfer concentrator modules 80.

In some implementations, the cumulative exposed surface area of thefront surfaces 88 can range between 50% and 80% of the total frontsurface area of the luminescent lateral transfer concentrator modules80. In some implementations, the cumulative exposed surface area of thefront surfaces 88 can range between 55% and 75% of the total frontsurface area of the luminescent lateral transfer concentrator modules80.

The dimensions of the intercell areas 78 (78 a, 78 b, and 78 c) can alsobe diverse. The intercell areas 78 a are shown in layouts 150 a and 150b to have length dimensions 160 that are the same; however, theintercell areas 78 a are shown to have different width dimensions 162.The length dimensions 160 and the width dimensions 162 of the intercellarea 78 a can range between 2 mm and 20 cm, independently. In someimplementations, the length dimensions 160 and/or the width dimensions162 can range between 2 mm and 10 cm, 2 mm and 500 mm, 2 mm and 100 mm,2 mm and 50 mm, 2 mm and 10 mm, 2 mm and 6 mm, or 2 mm and 4 mm. Thelength dimensions 160 can fall in different ranges than the widthdimensions 162.

In some implementations, the total intercell areas 78 can occupy from 2%(just filling in the “dead-space” in a standard module) up to 50% of thesurface area of the luminescent lateral transfer concentrator module 80.Thus, if the luminescent concentrator material 82 occupies onlyintercell areas 78, then the luminescent concentrator material 82 coversfrom 2 to 50% of the surface area of the luminescent lateral transferconcentrator module 80. In some implementations, the surface area of theluminescent lateral transfer concentrator module 80 is occupied by totalintercell areas 78 of 2 to 40%, 2 to 25%, 2 to 10%, 2 to 5%, 5 to 50%,10 to 50%, 25 to 50%, 40 to 50%, or 25 to 40%.

In some implementations, the luminescent concentrator material 82occupies the total intercell areas 78 by 50 to 100%, 65 to 100%, 80 to100%, 90 to 100%, 50 to 75%, or 65 to 80%. If the luminescentconcentrator material 82 overlays the photovoltaic material 84, then theluminescent concentrator material 82 can cover up to 100% of the surfacearea of the luminescent lateral transfer concentrator module 80. Theluminescent concentrator material 82 may occupy any area dimensions atthe periphery of the luminescent lateral transfer concentrator module80.

The photovoltaic material 84 used in the photovoltaic cells 86 caninclude, but is not limited to, one or more of: a-Si (amorphoussilicon), c-Si (crystalline silicon), mc-Si, thin-film Si,Al_(x)Ga_(1-x)As, Al_(x)Ga_(1-x)As_(y)N_(1-y), CdSe, CdS, CdZnTe,CuAlSe₂, CuGaS₂, CuGaSe₂, CuInAlSe₂,CuIn_(x)Ga_(1-x)S_((y)2)Se_((1-y)2), CuIn_(x)Ga_(1-x)Se₂,CuIn_(1-x)Ga_(x)Se_(2-y)S_(y), CuInS₂, CuInSe₂, CuO, CuZn_(x)Sn_(1-x)S₂,CuZn_(x)Sn_(1-x)Se₂, GaAs, Ga_(x)In_(1-x)As,Ga_(x)In_(1-x)As_(y)N_(1-y), Ga_(x)In_(1-x)P, In_(x)Ga_(1-x)N, InP,InP_(x)N_(1-x), Zn₃P₂, and ZnSe. In some embodiments, the photovoltaicmaterial 84 may employ quantum dot heterostructure materials asdisclosed in detail in U.S. patent application Ser. No. 12/606,908,entitled Solar Cell Constructed with Inorganic Quantum Dots andStructured Molecular Contacts, which is herein incorporated byreference. In preferred implementations, low-cost, well-established,and/or easily produced photovoltaic material 84, such as silicon-basedphotovoltaic materials 84 are employed. In some implementations,wafer-based Si (multicrystalline, ribbon, and crystalline) photovoltaiccells 86 are preferred, or cell based thin-film solar cells (having a“substrate configuration”) including, but not limited to, copper indiumgallium diselenide, copper indium gallium disulfide, copper indiumdisulfide, copper gallium diselenide, or any alloys of these arepreferred. In some implementations, standard c-silicon or mc-siliconphotovoltaic cells 86 are most preferred. The photovoltaic cells 86 maybe wired together in series and/or parallel.

In preferred implementations, the luminescent concentrator material 82includes luminescent chromophores dispersed in a transparent matrixmaterial 170. The transparent matrix material 170 preferably has anindex of refraction of n=1.1 to 3. In more preferred implementations,the transparent matrix material 170 has an index of refraction of n=1.5to 2. The transparent matrix material 170 may employ the same materialas, or different materials from, the spacer materials 140 and 148.

With reference again to FIGS. 4A, 4B, 4C, and 4D (collectively FIG. 4),photons 32 of light incident on the luminescent concentrator material 82are absorbed by the chromophores, re-emitted and ultimately directed viaTIR along reflected pathways 124 to the photovoltaic cells 86 on eitherside of the luminescent concentrator material 82. The luminescentchromophores can be either organic dyes or nanomaterials, such asquantum dot heterostructures (QDHs) as described later in greaterdetail. In some implementations, chromophores with inherently highphotoluminescence quantum yield (80% or above) are selected. In someimplementations, the chromophores have a photoluminescence quantum yieldof greater than 90%, greater than 95%, greater than 97%, or greater than99%. In some implementations, the chromophores are selected to haveminimal overlap between emission and absorption spectra to reduce oravoid re-absorption and another chance for loss by non-radiativerecombination or lost emission at an angle exceeding the critical anglefor TIR. Snell's law predicts that 75% of emitted light will beinternally reflected for materials with an index of refraction of ˜1.5,which is typical for glass and some solar cell encapsulants. In someimplementations of luminescent lateral transfer concentrator modules 80employing quantum dot hetero structures, as later described, only 12.8%of the incident light is below the critical angle for TIR.

The transparent matrix material 170 may include solar cell encapsulants,such as ethyl-vinyl acetate, polyvinylbutyral, polydimethyl siloxane,methacrylate polymers, cyclic olefin copolymers, may include metaloxides, such as TiO_(x), ZrO_(x), SiO_(x), ZnO_(x), etc., or may includeboth. The transparent matrix material 170 could be any of these orchemically modified versions of them (more or less OH groups, longer orshorter aliphatic solubilizing agents, etc.).

Organic dye chromophores include, but are not limited to, perylene orone of its derivatives, coumarin 6, and rhodamine or one of itsderivatives. In some implementations, the organic dye chromophore may beany dye with a photoluminescent quantum yield above 90% and a Stokes'shift above 50 nm.

Nanomaterials are highly suitable for use as the chromophores and offerserious advantages over dyes. The nanomaterials are solutionprocessible, highly controllable semiconductor nanostructuressynthesized by low-cost solution-based methods and can be made to havethe exact optical properties desired for the chromophores. Because oftheir unique structure and composition, nanomaterials can be more stablethan dyes. For example, the nanomaterials can be more reliable andprovide more predictable and precise absorption spectra.

Nanomaterials, such as semiconductor nanocrystals, are materials with atleast one nano-scale dimension, are most often grown colloidally, andhave been made in the form of dots, rods, tetrapods, and even moreexotic structures. (See Scher, E. C.; Manna, L.; Alivisatos, A. P.Philosophical Transactions of the Royal Society of London. Series A:Mathematical, Physical and Engineering Sciences 2003, 361, 241 andManna, L.; Milliron, D. J.; Meisel, A.; Scher, E. C.; Alivisatos, A. P.Nat Mater 2003, 2, 382-385.) Their sizes generally range from 3 nm to500 nm. Due to the quantum size effects which arise from a materialhaving dimensions on the order their electron's bohr radius, the bandgapof the material can also be tuned (See Alivisatos, A. P. J. Phys. Chem.1996, 100, 13226-13239 and Bawendi, M. G.; Steigerwald, M. L.; Brus, L.E. Annual Review of Physical Chemistry 1990, 41, 477-496.) In additionto facilitating tunability of the bandgap for absorption and emission,the nanomaterials have near perfect crystallinity, allowing them toattain extremely high photoluminescence (See Talapin, D. V.; Nelson, J.H.; Shevchenko, E. V.; Aloni, S.; Sadtler, B.; Alivisatos, A. P. NanoLett. 2007, 7, 2951-2959 and Xie, R.; Battaglia, D.; Peng, X. J. Am.Chem. Soc. 2007, 129, 15432-15433.)

In some implementations, the chromophores include nanomaterials,particularly nanocrystals such as quantum dot heterostructures. Quantumdot heterostructures are a form of nanomaterial engineered for aspecific application, such as absorption and emission, or downshiftingin particular. In some implementations, the chromophores includeencapsulated quantum dot heterostructures. In some implementations, thechromophores include quantum dot heterostructures, encapsulateddiscretely by secondary materials through a micelle approach.

FIG. 6 is an exemplary simplified enlarged drawing of an encapsulatedquantum dot heterostructure 180. With reference to FIG. 6, anencapsulated quantum dot heterostructure 180 includes a quantum dotheterostructure 180 having a core 182 surrounded by one or more shells184. The shell 184 is further encapsulated by an encapsulating material186.

By discretely encapsulating each quantum dot heterostructure 180individually, it is possible to homogeneously disperse the quantum dotheterostructures 180 in a transparent matrix material 170, as well asprotect the surface of the quantum dot heterostructures 180 from theexternal environment. Therefore, the use of the encapsulating materials186 greatly helps to both passivate surface defects of the quantum dotheterostructures and isolate the individual quantum dot heterostructures180 for better dispersion. Thus, the encapsulating materials 186minimize the interaction among the quantum dot heterostructures 180,improving the stability as well as the homogeneity in the transparentmatrix material 170. In some implementations, the encapsulatingmaterials 186 may be the same as the transparent matrix material 170 orthey may be derivatives of each other, or they may be differentmaterials. Good physical absorption between the materials 170 and 186are desirable to reduce the possibility of delamination.

The outer encapsulating materials 186 can be grown on individual quantumdot heterostructures 180 non-epitaxially. Micelles are formed using apair of polar and non-polar solvents in the presence of a compatiblesurfactant. The surface polarity of a quantum dot heterostructure 180can be modified so that only a single quantum dot heterostructure 180will reside in an individual micelle. By adding additional precursors,an inorganic or organic polymeric casing of encapsulating material 186can be selectively grown on the quantum dot heterostructure 180 insideof the micelle, which acts as a spherical template. (See Selvan, S. T.;Tan, T. T.; Ying, J. Y. Adv. Mater., 2005, 17, 1620-1625; Zhelev, Z.;Ohba, H.; Bakalova, R. J. Am. Chem. Soc., 2006, 128, 6324-6325; andQian, L.; Bera, D.; Tseng, T.-K.; Holloway, P. H. Appl. Phys. Lett.,2009, 94, 073112.)

Thus, by tuning the synthetic conditions, a single nanocrystal 180 canbe discretely incorporated in a silica sphere as shown in FIG. 6.Throughout the encapsulation process, the nanocrystal surfaces are wellpassivated to avoid any aggregation problems. Additionally, thispassivation endows the quantum dot heterostructures 180 withphotoluminescence quantum yields of and near unity. For the quantum dotheterostructures 180, the matrix compatibility can be dependent on thesurface of the encapsulating sphere, not the nanocrystal 180. Since thesurface of the encapsulating material 186 is spatially removed from thenanocrystal surface, alterations to the exterior of the encapsulatingmaterial 186 do not adversely affect the electronic or opticalproperties of the nanocrystal.

Semiconductor nanocrystals, such as cadmium selenide or indiumphosphide, have widely been studied for control over both theircomposition and shape. (See Scher, E. C.; Manna, L.; Alivisatos, A. P.Philosophical Transactions of the Royal Society of London. Series A:Mathematical, Physical and Engineering Sciences 2003, 361, 241 andTalapin, D. V.; Rogach, A. L.; Shevchenko, E. V.; Kornowski, A.; Haase,M.; Weller, H. J. Am. Chem. Soc 2002, 124, 5782-5790.)

Thus, in addition to spherically-shaped nanostructures, variousnon-spherical nanostructures have been demonstrated including, but notlimited to, nanorods, nanotetrapods, and nanosheets. Non-sphericalsemiconductor quantum dot heterostructures 180 have different uniquephysical and electronic properties from those of spherical semiconductornanocrystals. These properties can be employed advantageously in theluminescent concentrator material 82.

In some embodiments, the luminescent concentrator material 82 mayinclude individually encapsulated quantum dot heterostructures 180employing one type of core material, one type (composition) of shellmaterial, and one shape of shell material. In some embodiments, theluminescent concentrator material 82 may include individuallyencapsulated quantum dot heterostructures employing two or morevarieties of individually encapsulated quantum dot heterostructures,such as a first type of individually encapsulated quantum dotheterostructure employing a first type of core material, a first type ofshell material, and a first shape of shell material and a second type ofindividually encapsulated quantum dot heterostructure employing thefirst type of core material, the first type of shell material, and atleast one or more different shapes of shell material, such as rods andtetrapods.

In some embodiments, the second type of individually encapsulatedquantum dot heterostructure employs a first type of core material, atleast one or more different types of shell material, such as ZnS or CdS,and the first or at least one or more different shapes of shellmaterials. In such embodiments, each shell material may be associatedwith a specific shape, or each shell material may be formed with aplurality of shapes. In some embodiments, the second type individuallyencapsulated quantum dot heterostructures employs at least one or moredifferent types of core materials, the first or one or more differenttypes of shell materials, and the first or one or more different typesof shell shapes. In such embodiments, each core material may beassociated with specific shell materials and/or shapes, or each corematerial may be associated with one or more shell materials and/orshapes.

In some examples, the luminescent concentrator material 82 includesquantum dot heterostructures having CdSe dot cores 182 with a rod-shapedCdS shells 184, encapsulated in a silica encapsulating material 186.This quantum dot material exhibits maximum absorption at wavelengthsshorter than 500 nm and maximum emission at wavelengths between 550-700nm. In some examples, a CdS extended shell 184 is covered by a layer oforganic aliphatic ligands, with or without a silica encapsulatingmaterial 186. In some examples, an oxide layer is positioned between theCdS extended shell 184 and the organic ligands. In some implementations,the CdSe dot core 182 has no physical dimension greater than 6 nm, whilethe CdS extended shell 184 has at least one dimension greater than 15 nmand a second dimension about 1-2 nm thicker than the dimension of theCdSe dot core 182. In some implementations, the oxide shell can rangebetween 1 and 50 nm in radius (excluding the dimensions of the CdSe dotcores 182 and the CdS extended shell 184. In some implementations, theratio of shell volume to core volume falls between 1 and 1000, 1 and500, 1 and 100, 1 and 50, 1 and 20, 2 and 20, 2 and 50, 2 and 100, 2 and500, 5 and 500, 10 and 500, or 10 and 100. In some preferredimplementations, the ratio falls between 15 and 60. These variations anddimensional ranges may apply to other combinations of dot cores 182,shells 184, and encapsulating materials 186.

In some embodiments, the quantum dot heterostructures can include one ormore of the following inorganic compounds and/or any combination ofalloys between them: CdSe, CdS, CdTe, ZnSe, ZnS, ZnTe, CuS₂, CuSe₂,In₂S₃, In₂Se₃, CuGaSe₂, CuGaS₂, CuInS₂, CuInSe₂, PbSe, PbS, SiO₂, TiO₂,ZnO, ZrO. These materials can be arranged in cores 182, core-shells, andcore-shell-shells, with or without organic ligands, such as phosphonicacids, carboxylic acids, or amines. Any of these combinations can beimplemented in any of the above-disclosed spatial configurations anddimensions of luminescent concentrator material 82 and in combinationwith any of the disclosed photovoltaic materials 84.

Some examples of preferred core/shell combinations include, but are notlimited to, CdSe/CdS, CdSe/ZnS, InP/ZnS, and CuInSe/ZnS. In general,quantum dot heterostructures based on the II-VI chalcogenides are highefficiency emitters. In particular, quantum dot heterostructuresincluding CdSe, CdSe/ZnS, CdSe/CdS, or CdTe provide very highluminescence. In solution, these quantum dot heterostructure particleshave shown quantum efficiencies of greater than 90%, often as high as95%, and up to unity.

In some implementations, these quantum dot heterostructures have anabsorption cut-off of 500 nm and high extinction coefficients (10⁷ mol⁻¹cm⁻¹ at 340 nm). In some implementations, the optical properties of thequantum dot heterostructures have a ratio of the extinction coefficientsfor wavelengths less than 100 nm below the emission peak wavelength tothe extinction coefficient at the emission peak wavelength defined by:

$\frac{ɛ_{\lambda \leq {{\lambda\;{peak}} - 100}}}{ɛ_{\lambda\;{peak}}} \geq 100.$In other words, the extinction coefficient at the emission wavelength isless than 1% as high as the extinction coefficient at wavelengths 100 nmbelow the emission wavelength.

In some implementations, the quantum dot heterostructures have anemission between 580 and 700 nm with an extinction ratio of over 100. Insome implementations, the CdSe could be replaced by a material with alower energy gap (e.g., InAs, PbSe, PbS, CdTe, CdSeTe, or some CuInGaSealloys), and the CdS would be replaced by CdTe, InP, CdSeS or otherCuInSe alloys to enhance performance in a QuLLT architecture.

In some implementations, the nanomaterials have large Stokes shifts(greater than 50 nm for the spherical CdSe/CdS materials system) andeven larger effective Stokes shift (tunable by size), resulting inminimal self-absorption spectral overlap. This characteristic resultsfrom an absorption spectrum dominated by the CdS shell material, whichoccupies most of the quantum dot heterostructure volume, and an emissionspectrum determined primarily by the lower bandgap CdSe core. Bothabsorption and emission remain tunable through quantum size effects,allowing for efficient bandgap matching to the adjacent photovoltaicmaterial 84 of the photovoltaic cells 86 while also minimizing theself-absorption losses that critically hinder dye applications.

In some implementations, the absorption in the shell 184 is 10 to 500times, 25 to 250 times, or 30 to 100 times higher than the absorption inthe core 182. In the latter example, the implication is that there areat least 30 times more sulfur atoms than selenium atoms in such quantumdot heterostructures.

Additionally, the compatibility between the quantum dot heterostructuresand transparent matrix material can be controlled by chemicalmodifications to the surfaces of the shells 184 or the encapsulatingmaterial 186. Examples of modifications include: 1) suppression of thehydrophilic units to improve nanocrystal, shell, or encapsulatingmaterial compatibility with transparent matrix material and to improvedispersion stability; 2) introduction of chemical functional groups ableto coordinate/bind the nanocrystal, shell, or encapsulating materialsurfaces; and 3) extension of tunability of the mechanical propertiesthrough side chains variation. One example of this strategy is toreplace a certain percentage of acetate groups with hydroxyl groups onthe transparent matrix polymer. Fine tuning this percentage (from 1% to10%) can greatly increase the dispersion of the quantum dotheterostructures and increase the quantum yield of the luminescentconcentrator material 82.

In some implementations, the quantum dot heterostructures have aconcentration of 0.1 to 5 g/m² or 0.3 to 4 g/m² in the luminescentconcentrator material 82. In some implementations, for maximalefficiency of the luminescent lateral transfer concentrator modules 80,the quantum dot heterostructures have a concentration of 0.5 to 2 g/m²in the luminescent concentrator material 82. (This surface areaconcentration does not include the surface area of the luminescentlateral transfer solar concentrator module 80 that isn't covered by anythe luminescent concentrator material 82.) A concentration within thisrange will assure that maximal light absorption will occur in the shell184. As cost is a function of efficiency, this concentration range isalso ideal for lowering the cost of the luminescent lateral transfersolar concentrator module 80.

In some implementations, the emission range of the QDHs can be matchedto the peak absorption range of the photovoltaic material 84. Inparticular, the emission range of the QDHs can be adapted to peak within100 nm on one side of the peak absorption wavelength or range of thephotovoltaic material 84 and 50 nm on the other side of the peakabsorption wavelength or range of the photovoltaic material 84.

FIG. 7 is a graph showing the external quantum efficiency (EQE or QE)effect of the luminescent concentrator material 82 as a function ofwavelength for the photons 32 incident on the luminescent concentratormaterial at different distances from an mc-Si photovoltaic cell 86 in aluminescent lateral transfer solar concentrator module 80 employingquantum dot heterostructures; and FIG. 7 also shows the external quantumefficiency measurements for an mc-Si photovoltaic cell 86 in aluminescent lateral transfer solar concentrator module 80 employingquantum dot heterostructures. The luminescent lateral transfer solarconcentrator module 80 employing quantum dot heterostructures can beconveniently referred to as a quantum luminescent lateral transfer(QuLLT) solar concentrator module 80.

The external quantum efficiency is the percentage of the photons 32incident on the front surface 92 of the luminescent concentratormaterial 82 that will produce an electron hole-pair. As previouslydiscussed, the photons 32 incident on the luminescent concentratormaterial 82 in the intercell area 78 are re-emitted and directed alongreflection paths 124 into the photovoltaic material 84 of thephotovoltaic cells 86.

The response from intercell area 78 follows the fraction of absorbedlight in the luminescent concentrator material 82 and decreases withincreasing distance from the photovoltaic material 84. Because there area photovoltaic cells 86 on the other side of the intercell area 78, thecurrent generated in the intercell area 78 is double (half one way, halfthe other). The total current generated provides an effective efficiencyof 1% from the contribution from the luminescent concentrator material82. In some implementations, quantum dot heterostructures with shortbandgaps are preferred in order to utilize more of the solar spectrum.

With reference again to FIGS. 4B, 4C, and 4D, the spacer materials 140and 148 may employ the same material used for the transparent matrixmaterial 170. For some embodiments, it may be advantageous toincorporate optically downshifting materials into the spacer materials140 and 148. Such downshift materials may include downshiftingnanomaterials whose wavelength-shifting properties may be matched tooptimally cooperate with the primary absorption ranges of thephotovoltaic material 84. In particular, the downshifting nanomaterialsmay employ quantum dot heterostructures or encapsulated quantum dotheterostructures that have the same components and similar properties tothose already disclosed. In such embodiments of QuLLT solar modules 80that employ downshifting material, the downshifting material on top ofthe front surfaces 88 of the photovoltaic cells 86 can be different(absorb and emit at different wavelengths) from the luminescent material82 in the intercell areas 78 between the photovoltaic cells 86 making adual-color QuLLT solar module 80, which can conveniently referred to asa DCQuLLT solar module 80. Downshifting materials, particularlynanomaterials, and their relationships to photovoltaic materials arediscussed in detail in U.S. patent application Ser. No. 12/836,511,entitled Light Conversion Efficiency-Enhanced Solar Cell Fabricated withDownshifting Nanomaterial, which is herein incorporated by reference.

The QuLLT and DCQuLLT solar modules 80 can be fabricated byhigh-throughput, standard solar module-manufacturing techniques based onover 50 years of experience. For example, the luminescent concentratormaterial 82 (chromophore plus transparent matrix material 170) can beemployed in a QuLLT or DCQuLLT solar module 80 either by replacing astandard encapsulant with an extruded sheet, by printing (spray-coating,ink-jet, or screen-printing) onto the top sheet of glass 76, or byprinting directly on the photovoltaic cells 84 and on the intercell area78 of the bottom layer material 98.

Another way that a QuLLT or DCQuLLT solar module 80 has an advantageover an LSC module is in bottom line cost. The success many solarmodules depends on the total system costs as compared to the poweroutput of the module. The system cost is composed of the cost of thephotovoltaic cells 80, the cost of the luminescent concentrator material82, the balance of module (BOM) costs (glass, frame, encapuslants, andassembly), and the balance of system (BOS) costs (panel mounts,inverter, installation). The BOM and BOS costs are dependent on surfacearea.

LSC modules 40 are most efficient when coupled with InGaP photovoltaiccells on the basis of chromophore optical properties. Unfortunately,InGaP photovoltaic cells are prohibitively expensive at a practicalconcentration. An LSC InGaP module is a prime example in which the BOMand BOS costs are negligible compared to the costs of the photovoltaicmaterials and the photovoltaic cells.

An alternative is to reduce the photovoltaic cell cost by usingrelatively inexpensive photovoltaic cells 86, such as silicon-basedphotovoltaic cells (at a current cost of about $215/m²) at the expenseof power output per unit area (efficiency). The QuLLT solar modules 80are, therefore, the converse of an LSC InGaP module in that thephotovoltaic cell costs are negligible when compared to BOS and BOMcosts. The QuLLT and DCQuLLT solar modules 80 provide at least twice thepower per area that a LSC module 40 provides, greatly reducing the BOScosts.

The QuLLT and DCQuLLT solar modules 80 may have total system costs($/Watt) that are similar to standard silicon photovoltaic modulesbecause the photovoltaic cells, BOM, and BOS costs are more similar.Given the constraints of high photovoltaic cell cost per Watt of an LSCInGaP module and high BOM and BOS costs per Watt of standard siliconsolar cells, employing luminescent layers that laterally transfer andconcentrate light, via TIR, into inexpensive photovoltaic cells 86 in aquantum luminescent lateral transfer solar concentrator module 80 or adual color quantum luminescent lateral transfer solar concentratormodule 80 offers a cost-effective compromise. These modules 80 provide aminimum in cost per Watt by optimizing the fractions of the modules 80that are covered by high efficiency photovoltaic cells 86 and thefractions (intercell areas 78) that are covered by inexpensiveluminescent concentrator materials 82.

The QuLLT solar concentrator modules 80 offer flexibly to tailor thedesign of the modules 80 and its components to optimize system cost,regardless of fluctuations in price for photovoltaic cells 86,photovoltaic materials 84, luminescent concentrator materials 82, andmodule or system components. Furthermore, in the limit of rapidlydecreasing BOS and BOM costs, the technology developed is also directlytransferable to LSC modules. As a result, the cost per Watt provided bysolar concentrator modules 80 can do no worse than modules of either LSCor standard photovoltaic cells, optimizing high-efficiency and low-costbalance as the market dictates. Moreover, the QuLLT solar concentratormodules 80 can lower the total system cost by reducing the photovoltaiccell costs while maintaining higher efficiencies than LSC systems,thereby making the system less expensive than both LSC modules andstandard silicon modules.

FIGS. 8A, 8B, 8C (Collectively FIG. 8) and 9A, 9B, and 9C (CollectivelyFIG. 9) are correlated graphs show modeling of the relative costs andefficiencies for respective QuLLT and DCQuLLT solar concentrator modules80. The relative costs and efficiencies are dependent on chromophore andthe inter-cell spacing. With reference to FIGS. 8 and 9, the moduleefficiency (including frame, etc), the module costs ($/Watt), and theinstalled system costs ($/Watt) for both QuLLT and DCQuLLT modules arecompared. Industry standard estimates are used for balance of module(BOM) and balance of system (BOS) costs and an exemplary cost of $1/gramfor the luminescent chromophore. The dashed lines represent the valuesfor standard silicon solar modules.

Exemplary QuLLT solar concentrator modules 80 have already beenconstructed based on multicrystalline silicon solar cells and CdSe/CdSQDHs.

FIGS. 10A, 10B, and 10C show methods of fabricating QuLLT and DCQuLLTsolar concentrator modules. These modules can be fabricated in threeways. One involves embedding the quantum dot heterostructures orluminescent concentrator material 82 into a sheet of plastic that isthen laminated in addition to, or instead of, a standard solarencapsulant as shown in FIG. 10A. In another method, the luminescentconcentrator material 82 is printed onto the underside of standard solarglass (protective layer 76) as shown in FIG. 10B. In another method, theluminescent concentrator material 82 is printed onto the arrangedphotovoltaic cells 86 and optionally onto the front surface 96 of thebottom layer material 98. The luminescent concentrator material 82,photovoltaic cells 86, and bottom layer material 98 are then laminatedwith the encapsulant sheet and protective layer 76 as shown in FIG. 10C.

FIG. 11 is a photograph showing an experimental QuLLT submodule that hasbeen built. This prototype QuLLT module contains 2 mc-Si photovoltaiccells 86 separated by a 1 cm intercell area 78 a in which luminescentconcentrator material 82 has been deposited. The luminescentconcentrator material 82 also occupies intercell areas 78 b and 78 c.The quantum dot heterostructures in the luminescent concentratormaterial 82 is composed of a CdSe core 182 and a CdS shell 184.

In one exemplary module 80, the front surface 88 of the photovoltaicmaterial 84 includes silicon and occupies 43 to 91% of the front surfacearea of the module 80 and has optional length and width dimensions 108and 104 of greater than 100 mm. The intercell areas 78 make up 2 to 50%of the front surface area of the module 80, and at least 90% of theintercell areas 78 are occupied by a luminescent concentrator material82 which includes quantum dot heterostructures dispersed in atransparent matrix material 170 with an index of refraction n optimallybetween 1.5 and 2 at a concentration optimally between 0.5 and 2 g/m² ofsurface area of the luminescent concentrator material 82 (but theconcentration could be lower or higher). The quantum dotheterostructures typically exhibit average maximum peak absorption at awavelength length shorter than 500 nm, although that wavelength ismovable to optimally interact with (or not detract from) the activephotovoltaic cell 86 making up the module 80. The quantum dotheterostructures exhibit emission that is tunable between wavelengths580 and 700 nm, optionally contain a core 182 and a shell 184 thatprovide a ratio of core/shell extinction coefficients of between 1 and100, and optionally exhibit shell absorption that is 30 to 100 timegreater than core absorption. The quantum dot heterostructuresoptionally have a shell to core volume ratio of between 1 and 100. Anyone or more of these exemplary parameters can be substituted with anyrelated parameter disclosed herein to provide numerous optionalcombinations.

The QuLLT and DCQuLLT solar concentrator module 80 implementations maybe integrated with any of the layers or networks disclosed in U.S. Prov.Pat. Appl. No. 61/371,594, filed Aug. 6, 2010, entitled CooperativePhotovoltaic Networks Having Different Photovoltaic Materials, and inInternational Appl. No. PCT/US2011/045466, filed Jul. 27, 2011, entitledCooperative Photovoltaic Networks and Photovoltaic Cell Adaptations forUse therein, which are herein incorporated by reference. U.S. Prov. Pat.Appl. No. 61/410,754, filed Nov. 5, 2010, entitled Solar ModuleEmploying Quantum Luminescent Lateral Transfer Concentrator is alsoherein incorporated by reference.

It will be obvious to those having skill in the art that many changesmay be made to the details of the above-described embodiments withoutdeparting from the underlying principles of the invention. For example,it will be appreciated that subject matter revealed in any sentence,paragraph, implementation, example, or embodiment can be combined withsubject matter from some or all of the other sentences, paragraphs,implementations, examples, or embodiments except where such combinationsare mutually exclusive or inoperable. The scope of the present inventionshould, therefore, be determined only by the following claims.

The invention claimed is:
 1. A quantum dot, comprising: ananocrystalline core comprising a first semiconductor material; and oneor more nanocrystalline shells comprising a second, different,semiconductor material at least partially surrounding thenanocrystalline core, wherein an absorption spectrum and an emissionspectrum of the quantum dot are essentially non-overlapping.
 2. Thequantum dot of claim 1, wherein the quantum dot has a PLQY of at least90%.
 3. The quantum dot of claim 1, wherein the combination of thenanocrystalline core and the one or more nanocrystalline shells has anon-spherical geometry selected from the group consisting of a nanorod,a nanotetrapod, and a nanosheet.
 4. The quantum dot of claim 1, whereinthe first semiconductor material is selected from the group consistingof: CdSe, CdS, CdTe, ZnSe, ZnS, ZnTe, CuS₂, CuSe₂, In₂S₃, In₂Se₃,CuGaSe₂, CuGaS₂, CuInS₂, CuInSe₂, PbSe, PbS, SiO₂, TiO₂, ZnO, ZrO,and/or any combination of alloys therebetween.
 5. The quantum dot ofclaim 1, wherein the second semiconductor material is selected from thegroup consisting of: CdSe, CdS, CdTe, ZnSe, ZnS, ZnTe, CuS₂, CuSe₂,In₂S₃, In₂Se₃, CuGaSe₂, CuGaS₂, CuInS₂, CuInSe₂, PbSe, PbS, SiO₂, TiO₂,ZnO, ZrO, and/or any combination of alloys therebetween.
 6. The quantumdot of claim 5, further comprising a layer of organic aliphatic ligandscoupled to the one or more nanocrystalline shells, the ligands selectedfrom a group consisting of phosphoric acids, carboxylic acids, andamines.
 7. The quantum dot of claim 6, further comprising anencapsulating coating surrounding the nanocrystalline core and one ormore nanocrystalline shells, thereby creating an encapsulated quantumdot heterostructure (QDH).
 8. The encapsulated QDH of claim 7, whereinthe encapsulating coating passivates the nanocrystalline core and one ormore nanocrystalline shells.
 9. The encapsulated QDH of claim 7, whereinthe encapsulating coating is a silica coating.
 10. The encapsulated QDHof claim 9, wherein the silica coating is formed from a micelle.
 11. Theencapsulated QDH of claim 7, wherein the encapsulating coating has aradius approximately in the range of 1-50 nm, excluding the dimensionsof the nanocrystalline core and the one or more nanocrystalline shells.12. The quantum dot of claim 1, wherein the quantum dot has a maximumlight absorption at wavelengths less than approximately 500 nm, andmaximum light emission at wavelengths approximately in the range of550-700 nm.
 13. The quantum dot of claim 1, wherein the quantum dot hasan emission wavelength with an extinction coefficient less thanapproximately 1% as high as the extinction coefficient at a wavelength100 nm below the emission wavelength.
 14. The quantum dot of claim 1,wherein the one or more nanocrystalline shells has a light absorptionapproximately 10-500 times higher than that of the nanocrystalline core.15. The quantum dot of claim 1, wherein emission from thenanocrystalline core is at least approximately 75% of the total emissionfrom the quantum dot.
 16. The quantum dot of claim 1, wherein the firstsemiconductor material is selected from a group consisting of: InP andCuInSe, and wherein the second semiconductor material is ZnS.
 17. Thequantum dot of claim 1, wherein the quantum dot exhibits a Stokes shiftof greater than 50 nanometers.
 18. The quantum dot of claim 1, whereinthe nanocrystalline core has a first volume and the nanocrystallineshell has a second volume, and wherein the ratio of second volume to thefirst volume is in the range of 1 to
 100. 19. The quantum dot of claim1, wherein the nanocrystalline core has a first emission wavelengthextinction coefficient and the nanocrystalline shell has a secondemission wavelength extinction coefficient, and wherein the ratio of thesecond emission wavelength extinction coefficient to the first emissionwavelength extinction coefficient is in the range of 1 to
 100. 20. Thequantum dot of claim 1, wherein the nanocrystalline shell has a lightabsorption approximately 30-100 times higher than that of thenanocrystalline core.
 21. A luminescent material, comprising: atransparent matrix material; a plurality of encapsulated quantum dotheterostructures dispersed in the transparent matrix material, whereineach encapsulated quantum dot heterostructure comprises: ananocrystalline core comprising a first semiconductor material; one ormore nanocrystalline shells comprising a second, different,semiconductor material at least partially surrounding thenanocrystalline core; and an encapsulating coating surrounding thenanocrystalline core and one or more nanocrystalline shells, wherein anabsorption spectrum and an emission spectrum of the quantum dot areessentially non-overlapping.
 22. The luminescent material of claim 21,wherein a surface of the nanocrystalline core, a surface of the one ormore nanocrystalline shells, or a surface of the encapsulating coatingis chemically modified to suppress hydrophilic units to thereby improvecore, shell, or encapsulating material compatibility with thetransparent matrix material.
 23. The luminescent material of claim 21,wherein a surface of the nanocrystalline core, a surface of the one ormore nanocrystalline shells, or a surface of the encapsulating coatingis chemically modified to introduce chemical functional groups able tocoordinate or bind such surfaces.
 24. The luminescent material of claim21, wherein a mechanical property of a surface of the nanocrystallinecore, a mechanical property of a surface of the one or morenanocrystalline shells, or a mechanical property of a surface of theencapsulating coating is mechanically tuned to units to thereby improvecore, shell, or encapsulating material compatibility with thetransparent matrix material.
 25. The luminescent material according toclaim 21, wherein the matrix material is a transparent matrix polymerwith acetate groups, in which a certain percentage of acetate groups isreplaced with hydroxyl groups.